1. Field of the Invention
The present invention relates to a drop-on-demand multi-nozzle inkjet head having a plurality of nozzles, and also to an inkjet printing device including the inkjet head.
2. Related Art
Japanese Patent No. 3070625 proposes a technology for forming a dense arrangement of nozzles in an inkjet head by providing an array of long, thin protrusions on a diaphragm plate and using piezoelectric elements to deform the diaphragm plate through these protrusions. The protrusions on the diaphragm plate are formed of thin metal plates through etching or an electroforming method. Further, consideration has recently been given to a diaphragm plate having a two-layer construction, wherein a thin metal plate is laminated on a synthetic resin layer having excellent chemical resistance and protrusions are formed by etching a prescribed pattern in the metal layer, or else the protrusions are formed by electroforming a prescribed pattern on the synthetic resin layer. By deforming the diaphragm plate with piezoelectric elements through these protrusions, it is possible to establish a uniform surface area of the diaphragm plate that is pressurized by the piezoelectric elements. Further, by using a synthetic resin layer with excellent chemical resistance, it is possible to prevent ink from corroding the diaphragm plate.
U.S. Pat. No. 4,751,774 discloses a technology for bonding molded protruding members (feet) to the ends of transducer elements.
When bonding the diaphragm plate to a channel member, it is necessary to precisely align ink chambers formed in the channel member with the protrusions formed on the diaphragm plate in order to ensure stability and precision in producing and ejecting ink droplets. However, deviations in the relative positions of the channel member and the diaphragm plate tend to occur when the channel member is formed of a material with low thermal expansion, such as silicon, and the diaphragm plate is formed of a synthetic resin material with high thermal expansion. In this case, complex processes are required to position the members precisely, and the types of adhesives that can be used to bond the members are limited.
Further, when producing precise protrusions through etching or electroforming while achieving a dense arrangement of nozzles, the protrusions need to be formed thin, and so the resultant protrusions have less rigidity. For example, if the nozzles are arranged with a density of 75 nozzles per inch (npi) or greater, the rigidity of the protrusion is markedly lower, causing the protrusions to deform when the piezoelectric elements are driven to vibrate the diaphragm plate. Further, even if the ink chambers and the protrusions on the diaphragm plate are aligned precisely, the relative positions of the piezoelectric elements and a plate that supports the piezoelectric elements may become offset. There may be also deviation in the positions of active layers inside the piezoelectric elements. These positional deviations may cause the protrusions to apply pressure at positions off-center with respect to the ink chambers, preventing the protrusions from properly fulfilling their functions.
It is also difficult to bond the molded protruding members to the ends of transducer elements when the density of nozzles in the inkjet head is 75 npi or greater.